Blue OLED Emissive Layer Energy-Level Matching for Low Voltage
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Solution Overview
Problem
Developing a stable organic material with high triplet excited energy level for blue light-emitting elements has been challenging, leading to difficulties in achieving low power consumption and high emission efficiency.
Innovation Solution
A light-emitting element is designed with a host material and a guest material where the LUMO level of the guest material is lower than that of the host material, facilitating efficient energy transfer and conversion of triplet excitation energy into light emission, using iridium complexes with specific ligands for high electron-accepting properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If phosphorescent organic materials with high triplet excited energy levels are used for blue light emission, then light emission energy is improved, but material stability deteriorates
Solution Approach 1:
The patent introduces a host material as an intermediary between the electrodes and the phosphorescent guest material. The host material has higher triplet excited energy level than the guest material, allowing it to accept triplet excited states from the guest material and prevent direct electrode contact with high-energy phosphorescent materials, thereby stabilizing the system while maintaining blue light emission
Solution Approach 2:
The patent changes the energy level parameters of the host and guest materials specifically. The host material is selected with triplet excited energy level higher than the guest material's triplet excited energy level, creating an energy gradient that enables stable energy transfer and prevents material degradation while maintaining high light emission energy
2Illumination intensity
If energy difference between singlet and triplet excited states is increased to improve light emission energy, then light emission energy is improved, but driving voltage increases
Solution Approach 1:
The host material serves as an energy transfer intermediary that decouples the relationship between excitation energy and driving voltage. By using the host material with appropriate energy levels to mediate the energy transfer from electrodes to the phosphorescent guest material, the system achieves high light emission energy without requiring proportionally high driving voltage
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves low driving voltage, high emission efficiency, and improved reliability in light-emitting elements, particularly for blue light emission.
Implementation Method 1
light emission from the triplet excited state is referred to as phosphorescence. The guest material has a function of converting triplet excitation energy into light emission
Implementation Method 2
a host material that can efficiently excite a phosphorescent material. The energy difference between the LUMO level of the host material and the HOMO level of the host material is larger than or equal to light emission energy of the guest material
Implementation Method 3
By recombination of the injected electrons and holes, the organic material having a light-emitting property is brought into an excited state to provide light emission
Data Source
AI summary
To provide a light-emitting element with high emission efficiency and low driving voltage. The light-emitting element includes a guest material and a host material. A LUMO level of the guest material is lower than a LUMO level of the host material. An energy difference between the LUMO level and a HOMO level of the guest material is larger than an energy difference between the LUMO level and a HOMO level of the host material. The guest material has a function of converting triplet excitation energy into light emission. An energy difference between the LUMO level of the guest material and the HOMO level of the host material is larger than or equal to energy of light emission of the guest material.